1. Field of the Invention
The invention relates to electrical terminal blocks or strips made of a number of interlocking sections, and more particularly to a terminal block formed by a plurality of substantially identical sections interlocked longitudinally, each section providing means for establishing electrical connection to a junction point which is insulated from other electrical connections.
Sectional terminal blocks offer the advantage over one piece constructions in that it is not necessary to stock a large number of differing lengths of strip or block in order to satisfy interconnection requirements having different numbers of junctions. There is the further advantage that not all sections need to be completely identical, so long as they have a common design of interlocking mechanization. Thus, "feed-through" terminals can be intermixed with other styles of connections so that it becomes unnecessary to route certain conductors through a panel, at the same time that it is possible to maintain other electrical circuit points totally to one side of the panel so that there is uninterrupted shielding by the panel from the electrical circuit which is not connected to a feed-through.
In many applications it is important that a sectional terminal block be of substantially the same strength and rigidity as a one-piece block having the same number of connection sections. However, previously known sectional terminal blocks have offered less strength against separation of the sections or flexing of the length of the block than one-piece block constructions.
2. Description of the Prior Art
To provide the benefit of reduced inventory requirements, it has long been known to provide sectional terminal blocks which may readily be assembled to any desired length, where rigidity and strength of the assembled block are assured by the attachment of each of the sections to a length of track. Because the track need not be made of an insulated material, and because it may be fastened to a backing panel at a number of locations, a sectional terminal block such as that described in U.S. Pat. No. 3,293,593 eliminates concern about undue flexing of the assembled block. However, it is clear that if the track is made of a low cost, readily available material such as aluminum or steel, provision of a feed-through terminal connection becomes complicated, and requires that an appropriate size hole or holes be provided in the track.
A different form of sectional terminal block avoids the above described difficulties in providing feed-through connections, when the individual terminal sections rather than being mounted on a track are assembled in a slot in the panel or chassis itself, such as described in U.S. Pat. No. 3,315,215. However, it is clearly more time consuming and difficult to make a slot in the panel equal to the length of the desired terminal block than it is to provide a small number of holes for mounting screws, and in some applications the panel or chassis would not only be greatly weakened by cutting the slot, but a vital shielding effect of the chassis metal material would be lost.
Still another approach to terminal block design is exemplified by U.S. Pat. No. 2,922,139 which describes a block of identical sections, except for the end pieces, which requires neither a track nor a special panel slot. Mating projections and recesses provide alignment along both transverse axes. A press fit between certain longitudinal projections and the corresponding recess holds the sections together against longitudinal pulling or bowing of the assembled string of sections. However, it is clear that the strength of a long terminal block according to this design is limited by the resistance of the weakest force fit between a pin and a hole in the entire chain of sections. If some technique such as glueing is not utilized, the force required to assemble such a block will probably be substantially greater than the tensile force that the block can withstand.
An additional problem that has been considered is the protection and identification of connections. Because voltages appearing at exposed connections may be hazardous, and inadvertent contact with terminals may cause sensitive circuits to be damaged, removable covers such as shown in the U.S. Pat. No. 3,247,480 have been proposed. This cover has gripping fingers along each edge, arranged to slip over mating bosses on each section of the terminal assembly. The cover may be snapped free along one edge and pivoted upward about the cylindrical bosses of the other edge to expose the terminals or screw heads. However, such covers have had a relatively complex shape which is expensive to provide, and have required attachment surfaces on the terminal which substantially complicate molding shapes and may interfere with convenient use of the assembly.